EP0704837B1 - Hard disk head control - Google Patents
Hard disk head control Download PDFInfo
- Publication number
- EP0704837B1 EP0704837B1 EP95113531A EP95113531A EP0704837B1 EP 0704837 B1 EP0704837 B1 EP 0704837B1 EP 95113531 A EP95113531 A EP 95113531A EP 95113531 A EP95113531 A EP 95113531A EP 0704837 B1 EP0704837 B1 EP 0704837B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- disk
- head
- expansion
- control signal
- contraction
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Images
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B21/00—Head arrangements not specific to the method of recording or reproducing
- G11B21/02—Driving or moving of heads
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/60—Fluid-dynamic spacing of heads from record-carriers
- G11B5/6005—Specially adapted for spacing from a rotating disc using a fluid cushion
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
- G11B19/02—Control of operating function, e.g. switching from recording to reproducing
- G11B19/04—Arrangements for preventing, inhibiting, or warning against double recording on the same blank or against other recording or reproducing malfunctions
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B21/00—Head arrangements not specific to the method of recording or reproducing
- G11B21/16—Supporting the heads; Supporting the sockets for plug-in heads
- G11B21/20—Supporting the heads; Supporting the sockets for plug-in heads while the head is in operative position but stationary or permitting minor movements to follow irregularities in surface of record carrier
- G11B21/21—Supporting the heads; Supporting the sockets for plug-in heads while the head is in operative position but stationary or permitting minor movements to follow irregularities in surface of record carrier with provision for maintaining desired spacing of head from record carrier, e.g. fluid-dynamic spacing, slider
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B21/00—Head arrangements not specific to the method of recording or reproducing
- G11B21/02—Driving or moving of heads
- G11B21/12—Raising and lowering; Back-spacing or forward-spacing along track; Returning to starting position otherwise than during transducing operation
Definitions
- the present invention relates to the control of a head suspension in a hard disk drive (referred to as "HDD” hereinafter).
- the head of the HDD should have a constantly low flying height.
- the flying height is about 3.0-20 ⁇ .
- balance weighted head suspensions and the flying force of an ABS (Air Bearing Surface) of a slider are used.
- ABS Air Bearing Surface
- the head of the HDD is maintained at the low flying height when the spindle motor rotates at constant speed.
- the ABS of the head is contacted with the disk during the start/stop of the spindle motor. Friction between the ABS of the head and the disk generates dust which affects the HDD. Further, due to the dust, the life and reliability of the HDD are reduced.
- Such problems will be explained in detail with respect to Figs. 1 to 3.
- the control on the flying height being the interval between the magnetic head 161 and the disk 106, is disclosed in US Patent No. 5,012,369. Since the flying height is closely related to the high capacity and performance of the HDD, it is an important element in the HDD.
- the most probable operation in the magnetic write/read apparatus such as a HDD is performed such that the magnetic head 161 and the disk 106 contact each other at the same time.
- HDDs should preferably last for a long time, there should not be any abrasion when the magnetic head 161 and the disk 106 contact each other.
- the dust is generated due to abrasion when the magnetic head 161 and the disk 106 contact each other. Therefore, there are problems with the above method.
- one of the methods widely used in the prior art is to fly the magnetic head 161 on an air flow generated by rotation of the disk as shown in Fig. 3.
- a balance weight of the suspension 105 related to the shape of the head slider and the suspension 105 is used.
- the disk does not always rotate at constant speed, the linear velocity of the air flow in each position is different according to the radius of the HDD.
- the flying height becomes too high.
- the performance, capacity and endurance of the HDD have been increased by providing a skew angle between the direction of rotation of the disk 106 and the axial direction of the magnetic head 161.
- the disk 106 can contact the magnetic head 161 during the start or stop operation. That is, when starting the disk 106, by the time the rotation of the disk 106 arrives at a constant speed and the head 161 has thus "taken-off", the head 161 contacts the disk 106 to cause the head suspension to slide on the surface of the disk. Similarly when stopping in the stop of the disk 106, the disk is decelerated from the constant rotation speed, thus causing friction between the head and the disk, by the time the disk has completely stopped from the time the head 161 "lands".
- a parking area is set aside in which the head stops when the head 161 takes off from or lands on the surface of the disk 106.
- friction in the take-off/landing of the head still has a detrimental effect on the endurance of the HDD.
- additional problems arise. First, it is very difficult to rotate the disk 106 due to adsorption phenomena between the head 161 and the disk 106. Secondly, impurities generated by abrasion tend to damage the disk 106 and the head 161. This result in a scraping sound during the start/stop operations of the disk 106.
- US-A-4843502 which is reflected in the preamble of claim 1 describes a HDD in which the height of a head suspension is controlled by piezoelectric transducers, arranged to ensure that the magnetic head only approaches the disk surface once the disk has reached a speed sufficient to enable the head to "fly" above it.
- the piezoelectric transducers are controlled by the disk controller according to the state of the HDD.
- EP-A-0665548 which is only relevant under Art.54(3) already describes in a method of controlling a head suspension of a hard disk drive feedback means for generating a feedback signal corresponding to the degree of expansion or contraction of the expansion/contraction means and applying the control signal in dependence upon the feedback signal to maintain the separation of the head from the disk at a predetermined distance. It also describes separating the head from the disk during the starting or stopping of the disk rotation; however, it does not describe employing said feedback arrangement for separating the head from the disk during these periods (cf. e.g. col.12 1.40-51 and col.13 1.9-18).
- the present invention provides a method of controlling a head suspension in a hard disk drive which includes expansion/contraction means for controlling the height of the head suspension by expanding or contracting in response to a control signal, the method comprising applying a control signal to the expansion/contraction means to separate the head from the disk when the speed of rotation of the disk is below the speed required to generate sufficient air-flow to fly the head above the surface of the disk, characterized in that the hard disk drive further comprises feedback means for generating a feedback signal corresponding to the degree of expansion or contraction of the expansion/contraction means and the method comprises applying the control signal in dependence upon the feedback signal to maintain the separation of the head from the disk at a predetermined distance.
- the method may comprise the steps of:
- An initial step of parking the head in a parking area of the disk when the disk is stationary and a subsequent step of parking the head suspension by applying a stop signal to the actuator at or before the time the disk stops its rotation may be included.
- the present invention also provides apparatus for controlling a head suspension in a hard disk drive having a controller, the apparatus comprising means for generating a state signal according to a current disk operation function controlled by the controller, expansion/contraction means for controlling the height of the head suspension by expanding or contracting in response to a control signal and means for applying a control signal to the expansion/contraction means to separate the head from the disk in response to the state signal, when the speed of rotation of the disk is below the speed required to generate sufficient air-flow to fly the head above the surface of the disk characterized by feedback means for generating a feedback signal corresponding to the degree of expansion or contraction of the expansion/contraction means and means for applying the control signal in dependence upon the feedback signal to maintain the separation of the head from the disk at a predetermined distance.
- the apparatus may include amplifying means for amplifying the state signal, the expansion/contraction means being responsive to a signal which is generated in the said amplifying means.
- the expansion/contraction means may comprise a piezoelectric material, preferably a piezoelectric ceramic.
- the apparatus further comprises feedback mans for generating a feedback signal corresponding to the degree of expansion or contraction of the expansion/contraction means.
- the feedback means may comprise a piezoelectric ceramic.
- Fig. 4 shows one embodiment of the present invention.
- a piezoelectric material 700 is attached to an upper of a head suspension 105, and a control signal, as shown in Fig. 5 is generated from a controller 502 according to the rotation state of the disk 106.
- the control signal is amplified in a current amplifier 516 and applied to the piezoelectric material 700 through wire 401.
- the piezoelectric material 700 receiving the control signal which is generated in the controller 502 and amplified in the current amplifier 516, generates force so that the suspension 105 can be bent or curved by compression and extension caused by the piezoelectric phenomenon effect.
- the piezoelectric material 700 is capable of bending or curving the suspension 105 according to the characteristics thereof (Figs. 6A, 6B, 6C, 7A, 7B, and 7C).
- the force generated in the piezoelectric material 700 is transferred to the suspension 105 and enables the head 161 to separate from the disk 106 before/after the start and stop operations of the disk 106.
- the well known piezoelectric effect is utilised.
- the piezoelectric effect means that if pressure is exerted on any of the piezoelectric crystals, the material generates an electric field in proportion to the pressure. Conversely, if an electric field is applied to the crystals, the piezoelectric effect provides a change in the linear size caused by the electric field. Owing to this reversible connection relationship between mechanical energy and electric energy, piezoelectric materials are widely used in sound convertors, resonators, accelerometers, wave motion filters, photoelectric circuits, and photoelastic circuits etc.
- Fig. 6A when an electric field 601 is applied to the piezoelectric material 700, the piezoelectric material 700 is transformed by the resulting stress field 603. This is called the reverse direction effect of the piezoelectric material 700.
- Fig. 7A when a force 704 is applied to the piezoelectric material 700 from outside, electric charge 705 is distributed as shown in Fig.7B and an electric field 703 is generated as shown in Fig. 7C. This is called the forward direction effect.
- Fig. 8 illustrates another embodiment of the present invention, which shows a device for controlling the bend degree of the suspension 105 to which the piezoelectric material 700 is attached by expansion and extension of the piezoelectric element, the suspension 105 being a simple supporting element.
- a feed-back controller 800 if voltage is applied to one piezoelectric material 700 (an actuator) through a feed-back controller 800, an opposite piezoelectric material 700 used as a sensor is stretched or compressed to generate an electric field.
- the electric field is amplified in the current amplifier 516 and then input to the controller 502 through the wire 401.
- the controller 502 receives the output of the current amplifier 516 and manages the output according to the function of the HDD to apply the output to the feed-back controller 800. From this state, the controller 502 controls the degree of expansion/contraction the piezoelectric material 700 and thus controls the bend degree of the suspension 105.
- Figs. 9A to 9F help in explaining start/stop operations according to the present invention.
- the control through the embodiment according to the construction of Fig. 8 is illustrated.
- Fig. 9A shows an initial state in which the disk 106 is stationary.
- the piezoelectric material 700 is attached to the upper and lower portions of the suspension 105, and the head 161 is securely mounted in the parking area of the disk 106.
- the controller 502 recognizes that the disk 106 has stopped by the output of the current amplifier 516 or a function control state signal received through the wire 401. The control signal is thus not applied to the piezoelectric material 700 through the feed-back controller 800, so that the head, as shown in Fig. 9A, is securely mounted in the parking area of the disk.
- Fig. 9B shows the state just before the starting up of the disk 106.
- the controller 502 temporarily applies the electric field through the wire 402 from the feed-back controller 800 so that the piezoelectric material 700 is compressed.
- the suspension 105 is therefore bent to separate the head 161 from the surface of the disk 106.
- This state is sensed by the piezoelectric material 700 and then input to the controller 502 through the current amplifier 516.
- the controller 502 recognizes the input, and then starts and controls the disk.
- the flying height 801 or the time to reach flying height can be adjusted according to the characteristics of the controller 502 or the piezoelectric material 700.
- the controller 502 senses whether the rotation of the disk 106 reaches a constant speed or whether the disk 106 has sufficient speed to fly the head 161. In this state, the controller 502 applies the control signal to the piezoelectric material 700 through the feed-back controller 800 so that the head 161 is freely flown from the surface of the disk under control of the head 161.
- Fig. 9D shows the state just before the stop operation of the disk 106.
- the controller 502 applies the control signal to the piezoelectric material 700 through the feed-back controller 800 when the disk 106 is at lower speed than the speed required for flying the head, unlike Fig. 9C, so that force is added to the suspension 105 to separate the head 161 from the surface of the disk 105.
- Fig. 9E shows the state when the controller 502 applies the control signal to the piezoelectric material 700 by the time the disk 106 has completely stopped.
- Fig. 9F shows the state when the controller 502 frees the piezoelectric material 700 from the control signal after the disk has stopped, and the head 161 is securely mounted in the parking area of the disk 106.
- the piezoelectric material 700 is attached to the upper and lower ends of swiss arms 103 and can be used as shown in Fig. 10. Further, as shown in Fig. 8, the piezoelectric material are attached to the upper and lower ends of the swiss arms to be used as the feed-back controller 800.
- the present invention is advantageous in that the effective balance weight of the head suspension can be adjusted according to the control of the piezoelectric materials attached when the flying height is changed.
- the flying height can be controlled according to the radial position of the head on the surface of the disk, through retrial after failure of the initial operation among all the operations of the hard disk drive.
Description
Claims (8)
- A method of controlling a head suspension in a hard disk drive which includes expansion/contraction means for controlling the height of the head suspension by expanding or contracting in response to a control signal, the method comprising applying a control signal to the expansion/contraction means to separate the head from the disk when the speed of rotation of the disk is below the speed required to generate sufficient air-flow to fly the head above the surface of the disk;characterized in that the hard disk drive further comprises feedback means for generating a feedback signal corresponding to the degree of expansion or contraction of the expansion/contraction means; andthe method comprises applying the control signal in dependence upon the feedback signal to maintain the separation of the head from the disk at a predetermined distance.
- A method according to claim 1 comprising the steps of:separating the head from the disk by applying the said control signal when the disk is stationary;interrupting the said control signal when the speed of rotation of the disk arrives at that required to fly the head above the surface of the disk; andseparating the head from the disk by applying the said control signal when said disk speed drops below the speed required to fly the head above the surface of the disk.
- A method according to claim 2 and further comprising the initial step of parking the head in a parking area of the disk when the disk is stationary and the subsequent step of parking the head suspension by applying a stop signal to the actuator at or before the time the disk stops its rotation.
- Apparatus for controlling a head suspension in a hard disk drive having a controller, the apparatus comprising:means for generating a state signal according to a current disk operation function controlled by the controller;expansion/contraction means for controlling the height of the head suspension by expanding or contracting in response to a control signal; andmeans for applying a control signal to the expansion/contraction means to separate the head from the disk in response to the state signal when the speed of rotation of the disk is below the speed required to generate sufficient air-flow to fly the head above the surface of the disk;characterized by feedback means for generating a feedback signal corresponding to the degree of expansion or contraction of the expansion/contraction means; andmeans for applying the control signal in dependence upon the feedback signal to maintain the separation of the head from the disk at a predetermined distance.
- Apparatus according to claim 4 including amplifying means for amplifying the state signal, the expansion/contraction means being responsive to a signal which is generated in the said amplifying means.
- Apparatus according to claim 4 or claim 5, in which the expansion/ contraction means comprises a piezoelectric material.
- Apparatus according to claim 6, in which the piezoelectric material comprises a piezoelectric ceramic.
- Apparatus according to any one of claims 4-7 in which the means for generating a feedback signal comprises a piezoelectric ceramic.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
KR9422006 | 1994-09-01 | ||
KR1019940022006A KR0135111B1 (en) | 1994-09-01 | 1994-09-01 | Non contact start stop control method and apparatus of |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0704837A1 EP0704837A1 (en) | 1996-04-03 |
EP0704837B1 true EP0704837B1 (en) | 1998-10-07 |
Family
ID=19391844
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP95113531A Expired - Lifetime EP0704837B1 (en) | 1994-09-01 | 1995-08-29 | Hard disk head control |
Country Status (5)
Country | Link |
---|---|
US (1) | US5719720A (en) |
EP (1) | EP0704837B1 (en) |
JP (1) | JPH0877736A (en) |
KR (1) | KR0135111B1 (en) |
DE (1) | DE69505219T2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7082670B2 (en) | 1999-06-29 | 2006-08-01 | Hutchinson Technology, Inc. | Method for actively controlling the gram load on a disk drive suspension assembly |
Families Citing this family (23)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
KR100412059B1 (en) * | 1996-08-22 | 2004-04-14 | 삼성전자주식회사 | Device for realizing non-contact start stop function |
US6002549A (en) * | 1996-11-01 | 1999-12-14 | Seagate Technology, Inc. | Dither microactors for stiction release in magnetic disc drives |
KR100362158B1 (en) * | 1996-11-06 | 2003-02-19 | 삼성전자 주식회사 | Method for inspecting system preventing hard disk damage |
US5991114A (en) * | 1997-01-28 | 1999-11-23 | Seagate Technology, Inc. | Disc drive having gram load reducer and method of operating gram load reducer |
US6201668B1 (en) * | 1997-07-03 | 2001-03-13 | Seagate Technology Llc | Gimbal-level piezoelectric microactuator |
US6046884A (en) * | 1997-07-29 | 2000-04-04 | Seagate Technology, Inc. | Low mass disc drive suspension |
JP3030273B2 (en) * | 1997-11-28 | 2000-04-10 | インターナショナル・ビジネス・マシーンズ・コーポレイション | Disk drive device and control method therefor |
KR100505590B1 (en) * | 1998-01-15 | 2005-09-26 | 삼성전자주식회사 | Head landing control apparatus and method in hard disk drive |
US6667844B1 (en) * | 1998-09-25 | 2003-12-23 | Seagate Technology Llc | Active vibration suppression of glide head suspension arm |
US6163415A (en) * | 1999-04-02 | 2000-12-19 | Siros Technologies, Inc. | Loading and unloading a flying lens |
GB2373364B (en) * | 1999-12-02 | 2004-03-03 | Seagate Technology Llc | Fly height control over patterned media |
US6757124B2 (en) * | 1999-12-03 | 2004-06-29 | Seagate Technology Llc | Actuator system for a disc drive using a piezoelectric assembly |
JP3749081B2 (en) * | 2000-04-20 | 2006-02-22 | 富士通株式会社 | Head assembly and recording medium driving apparatus using microactuator |
US6590748B2 (en) | 2000-06-06 | 2003-07-08 | Seagate Technology Llc | Combined servo-tracking and preload-controlling microactuator |
US6568252B1 (en) | 2000-07-13 | 2003-05-27 | Seagate Technology Llc | Flyability and glide methodology for 100 GPSI |
US6760181B2 (en) | 2000-12-15 | 2004-07-06 | Seagate Technology Llc | Microactuator for dynamic controlling head-media interaction and fly-height |
US6819520B2 (en) * | 2000-12-22 | 2004-11-16 | Ic Mechanics, Inc. | Use of momentum transfer actuators for motion control of flexible mechanical structures |
JP3756109B2 (en) * | 2001-11-28 | 2006-03-15 | 富士通メディアデバイス株式会社 | Magnetic head support mechanism and magnetic head positioning control mechanism |
JP4170043B2 (en) * | 2002-08-13 | 2008-10-22 | 富士通株式会社 | Recording medium driving device |
US8004786B2 (en) * | 2006-02-17 | 2011-08-23 | Seagate Technology Llc | Transducer-data storage medium spacing adjustment |
US9373346B1 (en) | 2015-06-27 | 2016-06-21 | International Business Machines Corporation | Adjustable spacing formatter head |
US20220328068A1 (en) * | 2021-02-10 | 2022-10-13 | Seagate Technology Llc | Actuation of suspension for off ramp z-motion for an elevator drive |
US11948612B2 (en) | 2021-04-19 | 2024-04-02 | Seagate Technology Llc | Zero skew elevator system |
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US4605977A (en) * | 1983-12-14 | 1986-08-12 | Sperry Corporation | Air bearing head displacement sensor and positioner |
JPS60136073A (en) * | 1983-12-23 | 1985-07-19 | Hitachi Ltd | Magnetic disk device |
JPS62264489A (en) * | 1986-05-12 | 1987-11-17 | Mitsubishi Electric Corp | Disk device |
JPS62298978A (en) * | 1986-06-19 | 1987-12-26 | Nec Corp | Negative pressure using type floating head supporting mechanism |
JPS63108576A (en) * | 1986-10-27 | 1988-05-13 | Nec Corp | Loading mechanism for floating head |
JPS63187477A (en) * | 1987-01-30 | 1988-08-03 | Toshiba Corp | Magnetic head controller |
JPH01311481A (en) * | 1987-10-29 | 1989-12-15 | Sony Corp | Magnetic head device |
EP0342625B1 (en) | 1988-05-18 | 1994-03-23 | Fujitsu Limited | Head suspension mechanism for a recording apparatus |
JPH03113879A (en) * | 1989-09-26 | 1991-05-15 | Asahi Optical Co Ltd | Disk driving device |
JP2601553B2 (en) * | 1989-12-28 | 1997-04-16 | シャープ株式会社 | Magneto-optical recording / reproducing device |
US5060099A (en) * | 1990-04-05 | 1991-10-22 | Seagate Technology, Inc. | Disc drive slider lifter using shape memory metals |
JPH04129072A (en) * | 1990-09-18 | 1992-04-30 | Fujitsu Ltd | Magnetic disk device |
JPH04167276A (en) * | 1990-10-30 | 1992-06-15 | Teac Corp | Magnetic disk device |
US5313445A (en) * | 1991-03-01 | 1994-05-17 | Sharp Kabushiki Kaisha | Reproducing apparatus with suspension supporting a floating-type head with a bevelled slider |
JPH0547020A (en) * | 1991-08-09 | 1993-02-26 | Fuji Xerox Co Ltd | Optical disk device for information recording and reproducing |
JPH0684309A (en) * | 1992-09-04 | 1994-03-25 | Denki Kagaku Kogyo Kk | Magnetic head supporting device and controller |
US5377058A (en) * | 1992-12-31 | 1994-12-27 | International Business Machines Corporation | Fly height servo control of read/write head suspension |
KR960016899B1 (en) * | 1993-12-31 | 1996-12-26 | 삼성전자 주식회사 | Method and device for preventing impact of hdd |
-
1994
- 1994-09-01 KR KR1019940022006A patent/KR0135111B1/en not_active IP Right Cessation
-
1995
- 1995-08-29 DE DE69505219T patent/DE69505219T2/en not_active Expired - Lifetime
- 1995-08-29 EP EP95113531A patent/EP0704837B1/en not_active Expired - Lifetime
- 1995-08-31 US US08/522,155 patent/US5719720A/en not_active Expired - Lifetime
- 1995-08-31 JP JP7223701A patent/JPH0877736A/en active Pending
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7082670B2 (en) | 1999-06-29 | 2006-08-01 | Hutchinson Technology, Inc. | Method for actively controlling the gram load on a disk drive suspension assembly |
Also Published As
Publication number | Publication date |
---|---|
US5719720A (en) | 1998-02-17 |
DE69505219T2 (en) | 1999-06-02 |
KR0135111B1 (en) | 1998-04-22 |
EP0704837A1 (en) | 1996-04-03 |
JPH0877736A (en) | 1996-03-22 |
KR960011970A (en) | 1996-04-20 |
DE69505219D1 (en) | 1998-11-12 |
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